Method for improving light gauge building materials

ABSTRACT

A process is described in which non-structural galvanized steel studs are sequentially chemically treated with a permanganate coating to improve oxidation resistance, followed by treatment with a silicate coating sealant, optionally with zinc surface activation using an acid treatment.

BACKGROUND OF THE INVENTION

This invention relates to a process of making building materials adaptedfor use in building applications (preferably light gauge) in which thebuilding material has been preferably reduced in thickness yet meetsASTM standards or AISI standards (North American Standards forCold-Formed Steel Framing—General Provisions) for corrosion resistancefor building applications at a coating thickness which is essentiallyequal to or less than that specified for G-40 or equivalent corrosionresistance.

It has been common construction practice for many years to constructnon-load bearing walls and partitions in residential and commercialbuildings from formed sheet metal. These walls and partitions are, forexample, constructed of metal studs and floor and ceiling platestypically of 2″×4″ nominal dimensions, recognizing that other nominaldimensions are within the scope of this application, including but notlimited to ⅝″, 2 1/2″, 3 5/8″, 4″ and 6″.

Metal has advantages over wood as a material for vertical studs in thatmetal will not warp over time, will not be subject to termites and othervermin, and will consistently provide a flat surface to which material,such as drywall, forming the outer wall surfaces may be attached. Suchmetal construction, moreover, provides improved wind resistance forconstruction in areas at greater risk of hurricanes and tornadoes.Additionally, a metal stud is lighter than a wood stud therebyfacilitating construction practices. Notwithstanding the advantages ofmetal, wood has been the material of choice for the use as verticalnon-load bearing studs in substantial part because carpenters prefer itsuse in the assembly of walls and partitions. One reason for thispreference is due to the fact that galvanized (zinc coated) metal usedin metal building studs has a tendency to rapidly develop a white filmof zinc oxide or hydroxide.

It is well known that steel rusts when left unprotected in almost anyenvironment. Applying a thin coating of zinc to steel is an effectiveand economical way to protect steel from corrosion. Zinc coatingsprotect steel by providing a physical barrier as well as cathodicprotection to the underlying steel. The main mechanism by whichgalvanized coatings protect steel is by providing an impervious barrierthat does not allow moisture to contact the steel. Without moisture (thenecessary electrolyte), there is no corrosion. However, zinc is areactive metal and will corrode slowly over time. For this reason, theprotection offered by galvanized coatings is proportional to the coatingthickness. When base steel is exposed, e.g., by cutting or scratching,the steel is protected by the sacrificial corrosion of the zinc coatingadjacent to the steel. This is due to the fact that zinc is moreelectronegative (more reactive) than steel in the galvanic series.

Historically, galvanizing has proven to be the most economical andeffective way to protect steel formed in to metal studs and otherbuilding framing components. Galvanizing is a process where steel sheetis immersed into a bath of molten zinc (e.g., 850° F.) to form ametallurgically bonded zinc coating. The continuous galvanizing processcan apply a number of different coatings that vary in thickness,appearance and alloy composition. The term “galvanized” refers to thestandard continuous coating that is basically zinc. About 0.2% aluminumis added to the galvanizing bath to form a thin, inhibitingiron-aluminum layer on the steel surface that ensures formation of thezinc coating. The finished coating has good formability and corrosionresistance, and provides excellent sacrificial protection. In someapplications, the zinc coating is applied in conjunction with annealingof the metal and these products are often referred to as galvannealedproducts.

The present method herein described is applicable not only to galvanizedsteel, but also to steel which has been subjected to a Galvalume®process, in which carbon steel sheet is coated with an aluminum-zincalloy by a continuous hot-dipped process. The nominal coatingcomposition is about 55% aluminum and 45% zinc plus a small addition ofsilicon (added to at least improve coating adhesion to the steelsubstrate). Similarly, the present invention may be utilized withaluminized coatings. Additionally, the present method is applicable togalvannealed carbon steel, which is steel which has been coated withzinc by a hot-dipped process which converts the coating into a zinc-ironalloy. Conversion to this alloy results in a non-spangle matte finishwhich makes the sheet suitable for painting after fabrication.

Most light gauge steel is galvanized by unwinding coils of cold rolledsteel sheet and feeding the sheet continuously through a molten zincbath at speeds up to 600 feet per minute. The specified coatingthickness is controlled by air “knives” which blow off the excesscoating deposited on the steel as it exits the molten zinc bath. Therecommended minimum coating requirements for non-load bearing(non-structural) framing members is given with reference to ASTM A 653(Standard Specification for Steel Sheet) ASTM C 645 (StandardSpecification for Non-Structural Steel Framing Members) and A1003(Standard Specification for Steel Sheet Carbon, Metallic- andNonmetallic-Coated for Cold-Formed Framing Members). The durability ofzinc based coatings is often a function of the amount of wetness (ordampness) of the installation location and the composition of theatmosphere. Water leakage, excessive humidity or condensation willdamage any construction material over time, and it will also acceleratethe corrosion of galvanized coatings.

The ability of a zinc coating to protect steel depends on zinc'scorrosion rate. Freshly exposed galvanized steel reacts with thesurrounding atmosphere to form a series of zinc corrosion products. Inair, newly exposed zinc reacts with oxygen to form a very thin zincoxide layer. When moisture is present, zinc reacts with water resultingin the formation of zinc hydroxide. A final common corrosion product toform with exposure to the atmosphere is zinc carbonate as zinc hydroxidereacts with carbon dioxide in the air.

In use, galvanized sheet steel is passivated and recoiled for shipmentto the fabricator, where the steel sheets are cut and formed in thedesired shapes of studs and other light gauge building components. Asknown in the industry, “white rust” or “white storage stain” istypically manifested as a bulky, white, powdery deposit that formsrapidly on the surface of galvanized coatings under certain conditions.These corrosion products will cause many deleterious effects. Forexample, zinc oxide prevents paint from adhering to the metal as well asaccelerates further corrosion of the metal which is unsightly to anygalvanized coating's appearance. Pure water contains essentially nodissolved minerals and the zinc will react quickly with pure water toform zinc hydroxide, a bulky white and relatively unstable oxide ofzinc. Where freshly galvanized steel is exposed to pure water (e.g.,rain, dew or condensation, etc.) particularly in an oxygen-deficientenvironment, the water will continue to react with the zinc andprogressively consume the coating. The most common condition in whichwhite rust occurs is with galvanized products that are nested together,tightly packed, or when water can penetrate between the items and remainfor extended periods of time. It is recognized that while “white rust”is relevant for galvanized steel, Galvalume® oxidation products rustblack while galvannealed products rust red or orange due at least inpart to the iron filings in the coating.

There are a number of steps that can reduce the formation of white rustor other oxidation products. These include keeping the packed work dry,packing the items to permit air circulation between the surfaces,stacking the packed items to allow water to drain, and treating thesurface with water repellent or barrier coatings to prevent moisturecontact with the galvanized surface. This invention pertains to thelast-mentioned solution.

Passivating a galvanized metal prevents the formation of zinc oxide orhydroxide. Typical passivating solutions utilize a dichromate orchromate composition. These compositions are typically applied to themetal via immersion. An untreated surface will show signs of corrosionafter 0.5 hours of exposure to a neutral salt spray according to ASTMspecification “B 117” and a thin chromate film produced by a dipprocedure will show signs of corrosion after 12 to 75 hours of saltspray exposure (see ASTM specification “B 201”).

The prior art advantages of an applied chromation were so important thatalmost all galvanized metal building products have been chromate coated.The prior art is believed to include four chromations named after theircolorations, which are each applied by treating (immersion, spraying,rolling) a zinc-plated surface with the corresponding aqueous chromatecoating solution. Moreover yellow and green chromations for aluminum areknown which are produced analogously. In any case, these are variouslythick layers of substantially amorphous zinc/chromium oxide (oraluminum/chromium oxide) with non-stoichiometric compositions, certainwater content, and inserted foreign ions. These are known and classifiedinto method groups in accordance with German Industrial Standard (DIN)50960, Part 1.

Colorless and Blue Chromations: The blue chromate layer has a thicknessof up to 80 nm, is weakly blue in its inherent color and presents agolden, reddish, bluish, greenish or yellow iridescent coloring broughtabout by refraction of light in accordance with layer thicknesses. Verythin chromate layers lacking almost any inherent color are referred toas colorless chromations. The chromate coating solution may in eithercase consist of hexavalent as well as trivalent chromates and mixturesof both, moreover conducting salts and mineral acids. There arefluoride-containing and fluoride-free variants. Application of thechromate coating solutions is performed at room temperature. Thecorrosion protection of unmarred blue chromations amounts to 10-40 hoursin the salt spray cabinet according to DIN 50021 SS until the firstappearance of corrosion products.

Yellow Chromations: The yellow chromate layer has a thickness of about0.25-1 μu, a golden yellow coloring, and frequently a strongly red-greeniridescent coloring. The chromate coating solution substantiallyconsists of hexavalent chromate, conducting salts and mineral acidsdissolved in water. The yellow coloring is caused by the significantproportion (80-220 mg/m²) of hexavalent chromium which is insertedbesides the trivalent chromium produced by reduction in the course ofthe layer formation reaction. Application of the chromate coatingsolutions is performed at room temperature. The corrosion protection ofunmarred yellow chromations amounts to 100-200 hours in the salt spraycabinet according to DIN 50021 SS until the first appearance ofcorrosion products.

Olive Chromations: The typical olive chromate layer has a thickness ofup to 1.5 μu and is opaquely olive green to olive brown. The chromatecoating solution substantially consists of hexavalent chromate,conducting salts and mineral acids dissolved in water, in particularphosphates or phosphoric acid, and may also contain formates. Into thelayer considerable amounts of chromium(VI) (300-400 mg/m²) are inserted.Application of the chromate coating solutions is performed at roomtemperature. The corrosion protection of unmarred olive chromationsamounts to 200-400 hours in the salt spray cabinet according to DIN50021 SS until the first appearance of corrosion products.

Black Chromations: The black chromate layer is fundamentally a yellow orolive chromation having colloidal silver inserted as a pigment. Thechromate coating solutions have about the same composition as yellow orolive chromations and additionally contain silver ions. With a suitablecomposition of the chromate coating solution on zinc alloy layers suchas Zn/Fe, Zn/Ni or Zn/Co, iron, nickel or cobalt oxide will beincorporated into the chromate layer as a black pigment so that silveris not required in these cases. Into the chromate layers considerableamounts of chromium(VI) are inserted, namely between 80 and 400 mg/m²depending on whether the basis is a yellow or olive chromation.Application of the chromate coating solutions is performed at roomtemperature. The corrosion protection of unmarred black chromations onzinc amounts to 50-150 hours in the salt spray cabinet according to DIN50021 SS until the first appearance of corrosion products.

In accordance with the prior art, thick chromate layers affording highcorrosion protection>100 hours in the salt spray cabinet according toDIN 50021 SS or ASTM B 117-73 until the appearance of first corrosionproducts according to DIN 50961 (June 1987) Chapter 10, in particularChapter 10.2.1.2, in the absence of sealing or any other particularafter treatment (DIN 50961, Chapter 9) may only be produced by treatmentwith dissolved, markedly toxic chromium(VI) compounds. Accordingly thechromate layers having the named requirements to corrosion protectionstill retain these markedly toxic and carcinogenic chromium(VI)compounds, which are, moreover, not entirely immobilized in the layer.

Reliance on hexavalent or trivalent chromium has many drawbacks.Hexavalent chromium is extremely toxic and as such more costly to workwith. Hexavalent chromium will require special disposal procedures.Therefore, there is a need for a chromium-free coating for zinc surfaces(e.g., galvanized steel), particularly for galvanized steel studs whichare used in non-structural applications where the thickness of thegalvanized steel has been thinned so as to permit the fabrication ofadditional linear feet of product.

The present method herein described is applicable not only to galvanizedsteel, but also to steel which has been subjected to a Galvalume®process, in which carbon steel sheet is coated with an aluminum-zincalloy by a continuous hot-dipped process. The nominal coatingcomposition is about 55% aluminum and 45% zinc plus a small addition ofsilicon (added to at least improve coating adhesion to the steelsubstrate). Similarly, the present invention may be utilized withaluminized coatings. Additionally, the present method is applicable togalvannealed carbon steel, which is steel which has been coated withzinc by a hot-dipped process which converts the coating into a zinc-ironalloy. Conversion to this alloy results in a non-spangle matte finishwhich makes the sheet suitable for painting after fabrication.

The sequentially applied coatings (preferably without drying betweencoating application) of the present invention represent an improvementover commercially available corrosion-inhibiting pigments includingcompounds such as molybdates, phosphates, silicates, cyanamides, andborates that have no inherent oxidizing character that have been used asalternatives to chromate pigments. Coatings that contain these materialscan effectively inhibit corrosion as barrier films until the coating isbreached, as by a scratch or other flaw. Films or coating that do notcontain oxidizing species can actually enhance corrosion on a surfaceafter failure due to the effects of crevice corrosion.

SUMMARY OF THE INVENTION

A process is described for making a corrosion-resistant metal buildingcomponent is disclosed comprising the steps of:

-   -   providing a steel sheet (preferably galvanized, but also which        has been subjected to a Galvalume® and/or aluminizing process        and/or galvannealed processing) suitable for use in making metal        building components having an initial thickness,    -   rolling the steel sheet by at least approximately 10% (up to        approximately 65%) to form a thinner steel sheet,    -   forming said steel sheet into at least one reduced thickness        metal building component,    -   applying a first permanganate coating composition wherein        permanganate is the major active component by weight containing        essentially no hexavalent or trivalent chromium to at least one        surface of said building component, said coating composition        preferably being an alkali earth metal permanganate wherein said        alkali earth metal is selected from the group consisting of        potassium, sodium, lithium, cesium and rubidium and applied at a        pH of about from 9.0 to 2.0 inclusive, and    -   applying a second silicate sealant composition (preferably an        alkali metal silicate sealant, wherein the alkali metal is        selected from the group consisting of potassium, sodium,        lithium, cesium and rubidium (preferably K)) such that the        building component meets the ASTM C 645-08a or equivalent        standard (or AISI specification) at a coating weight which        approximately equal to or less than that specified by ASTM A        1003-G40.

In another embodiment, a process is disclosed for making acorrosion-resistant building component comprising the steps of:

-   -   providing a steel sheet suitable for use in making metal        building components, said sheet having a surface comprising zinc        or a zinc alloy, suitable for use in making metal building        components having an initial thickness,    -   applying a first coating composition comprising a permanganate        composition (preferably an alkali metal permanganate composition        wherein said alkali metal of said permanganate composition is        selected from the group consisting of potassium, sodium,        lithium, rubidium and cesium) containing essentially no        trivalent or hexavalent chromium to said building component, and        wherein said and applied at a pH of about 9.0 to 2.0 inclusive;    -   applying a second coating composition comprising a silicate        sealant composition to the building component (preferably an        alkali metal silicate composition wherein said alkali metal of        said permanganate composition is selected from the group        consisting of potassium, sodium, lithium, rubidium and cesium);    -   reducing a thickness of said steel sheet by at least        approximately 10% (optionally up to approximately 65%);    -   forming said reduced thickness steel sheet into at least one        metal building component and wherein said building material        meets the ASTM C 645-08a or equivalent standard (e.g., AISI        General Provision Standard) at a coating weight which is        approximately equal to or less than that specified by ASTM A        1003-G40.

In yet another embodiment, a process is disclosed for making acorrosion-resistant galvanized building component comprising the furtherstep of cleaning the surface of the metal building component, whichpreferably is galvanized, but also which may have been subjected to aGalvalume® and/or aluminizing process and/or galvannealed processing)with a cleaning agent, more preferably acidic, most preferably an acidselected from the group consisting of HCl, H₂SO₄, and H₃PO₄.

As used in this application, the silicate composition is preferably analkali metal silicate composition, and most preferably a water-solublesilicate salt, which in the potassium form has a chemical formula ofK₂SiO₃. The properties of liquid potassium silicates are dependent uponthe SiO₂/K₂O weight ratios. The potassium silicates are similar tosodium silicates.

Silicates are converted to solid films or bonds by two methods: (1)evaporation of water (dehydration) or (2) chemical setting mechanism.These can be used separately or in combination. Chemical setting isoften used to improve film moisture resistance, to reduce setting time,and to increase ultimate bond strength as needed.

As water evaporates, liquid silicates become progressively tackier andmore viscous. As the dehydration continues, the silicate is brought intoa final hardened condition. Soluble silicates are formed with higherSiO₂/Na₂O or SiO₂/K₂O ratios. The higher ratio silicates change from analmost water-like condition to a semi-solid state when only a smallamount of water is evaporated. Lower ratio silicates, such as sodiumsilicates, dehydrate more slowly, because their higher alkali contentcreates a greater affinity for water. Flexibility increases inlower-ratio silicates because of their tendency to hold onto water moretenaciously than higher ratio silicates and thus have some degree ofinternal plasticization of the film by the residual water. Because thelow-ratio silicates tend to retain more water, they are less brittlethan the higher ratio silicates.

Silicate films are subject to moisture pick-up and degradation. However,this process can be slowed if water is completely removed from thesilicate. Air drying alone usually is not adequate for films or bondsthat will be exposed to weather or high moisture conditions. For suchapplications, heat is usually recommended. Initially, the temperatureshould be increased gradually to 200-210° F. to slowly remove excesswater. Then final curing can be done at least 350-700° F. Heating tooquickly may cause steam to form within the film, resulting in blisteringor puffing when the steam is released. For some applications, where aninsulated coating is desired, this intumescent property can be useful.Infrared and microwave heating have been used successfully for hardeningsilicate systems.

Silicate coatings and adhesives are inorganic aqueous polymers and theyperform most effectively on hydrophilic, non-oily surfaces, where theyachieve proper wetting and, hence, maximum adhesion. Generally, a thincontinuous silicate film between the surfaces to be bonded providesoptimum adhesion.

When coating or bonding metals and other similar rigid materials, thedifference in coefficient of thermal expansion between silicate and thebonded surfaces is important. However, where temperatures are relativelyconstant and there is no mechanical strain, ultrathin silicate filmswhich have been dehydrated by baking can hold permanently. A thinsilicate film has greater elasticity and is more serviceable than athick one for coating or bonding metal. A compatible surfactant in theamount of 0.05-0.1% by weight relative to the silicate will aid surfacewetting. Good adhesion to metal often can be obtained after the surfacehas been thoroughly cleaned with alkali or acid or solvent or isdegreased or sandblasted.

In a preferred embodiment, the building component after sequentialcoating with the two compositions (permanganate followed by silicate),will meet the ASTM C 645-08a standard at a coating weight which is equalto or less than that specified by ASTM A 1003-G40.

The non-structural building component comprises at least zinc in acoating or alloy, preferably galvanized metal building stud. The initialsteel thickness may range from 0.017 inch (17 mils) in thickness to0.115 inch (115 mils) where the products are metal studs.

The rolling step may be done with a thickness reduction of at least 10%,more preferably 20% and most preferably at least 25% up to approximatelya 65% reduction in thickness. Stated another way, galvanized steel sheetmay reduced in thickness by at least 10%, more preferably 20%, and mostpreferably by 25% prior to the application of the conversion coating ofthe present process. However, reductions in thickness to as thin as 14mils are within the scope of this invention.

In one embodiment of this invention, the rolling step may be performedafter the sequential application of the coatings (permanganate followedby silicate) and the final product will meet the ASTM C 645-08a standardat a coating thickness which is equal to or less than that specified byASTM A 1003-G40. The rolling step may be done with a thickness reductionof at least 10%, more preferably 20% and most preferably at least 25% upto approximately a 65% reduction in thickness.

The present method eliminates the need for hexavalent chromiumcompositions which, due to their toxicity, are being forced out of theworkplace environment. Rather, the invention provides protectivecoatings which are sequentially applied which have compositions ofpermanganic acids and silicates.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 (a) through (c) are a series of photographic depictions of agalvannealed panel at its original 28 mils thickness after exposure tosalt spray for 24, 48 and 75 hours for panels which have been coatedwith the permanganate composition of this invention at a concentrationof 0% (no coating), 20% concentration (80% diluted), 50% concentration(50% diluted) and 80% concentration (20% diluted);

FIGS. 2 (a) through (c) are a series similar to FIG. 1 wherein thegalvannealed panel has been reduced in thickness from 28 mils to 24 mils(about a 15% reduction in thickness);

FIGS. 3 (a) through (c) are a series similar to FIG. 2 wherein thegalvannealed panel has been reduced in thickness from 28 mils to 22 mils(about a 20% reduction in thickness);

FIGS. 4 (a) through (c) are a series similar to FIG. 3 wherein thegalvannealed panel has been reduced in thickness from 28 mils to 21 mils(about a 25% reduction in thickness);

FIGS. 5 (a) through (n) are a series of photographic depictions of steelpanels at 24 hours of salt spray exposure and wherein FIG. 5( a) is acertified G-40 sample derived from flat steel used as a test comparativeknown to meet ASTM specification of G-40 for non-structural framing;FIG. 5( b) is a head end of slit coil used for formed Ultra® steelsample (as hereinbelow described) which had been galvannealed with A45coating pursuant to ASTM A 653/A 653M-08 and reduced in thickness from0.029″ to 0.0245″; FIG. 5( c) is a second sample of a tail end of slitcoil used for formed Ultra® steel sample; FIG. 5( d) is a head end ofslit coil used for formed flat steel sample which had been galvannealedwith A45 coating (total coating weight of 0.316-45 g/m² and reduced inthickness from 0.029″ to 0.0245″; FIG. 5( e) is a second sample of atail end of slit coil used for formed flat steel sample similarlyreduced in thickness; FIG. 5( f) is an additional tail end of slit coilsample used for formed flat steel sample; FIG. 5( g) is a flat steelsample of cold worked with Ultra® steel process before forming into astud (head of coil); FIG. 5( h) is a second sample of flat cold workedwith Ultra® steel process before forming into a stud (head of coil);FIG. 5( i) is a flat steel sample of cold worked with Ultra® steelprocess before forming into a stud (tail of coil); FIG. 5( j) is asecond sample of flat cold worked with Ultra® steel process beforeforming into stud (tail of coil); FIG. 5( k) is a sample of formedUltra® steel stud (head of coil); FIG. 5( l) is a sample of formedUltra® steel stud (tail of coil); FIG. 5( m) is a sample of formed flatsteel stud (head of coil); and FIG. 5( n) is a sample of formed flatsteel stud (tail of coil);

FIGS. 6 (a) through (n) are a series of photographic depictions of steelpanels at 48 hours of salt spray exposure using the series of panels ofFIG. 5.

FIGS. 7 (a) through (d) are a series of photographic depictions of steelpanels at 75 hours of salt spray exposure using the series of panels ofFIG. 5;

FIGS. 8 (a) through (d) are a series of photographic depictions of steelpanels at 96 hours of salt spray exposure using the series of panels ofFIG. 5;

FIGS. 9 (a) and 9 (b) are photographic depictions of galvannealed steelpanels which were treated by a sequential application of a 0.8%permanganate solution applied in a bath at 140° F. for approximately 4seconds followed by 3.0% silicate solution at a bath temperature of 80°F. for approximately 4 seconds followed by a cold reduction in thicknessfrom 0.295″ to 0.244″ in which FIG. 9 (a) was bent approximately 60-75°after treatment and each panel was subjected to a 75 hour salt spraytest in accordance with ASTM B-117-07a;

FIGS. 10 (a) and 10 (b) are photographic depictions of galvannealedsteel panels, in which the panel in FIG. 10 (b) was treated by asequential combination of a 0.8% permanganate solution applied in a bathat 140° F. for approximately 4 seconds followed by 3.0% silicatesolution at a bath temperature of 80° F. for approximately 4 secondsfollowed by a cold reduction in thickness from 0.028″ to 0.021″, thensubject to a 75 hour salt spray test in accordance with ASTM B-117-07awhile FIG. 10 (a) illustrates a steel panel which was not subject to anypretreatment and subject to a 75 hour salt spray test in accordance withASTM B-117-07a;

FIGS. 11 (a) and 11 (b) are photographic depictions of the implicationsof drying between the sequential application of coatings, in which thegalvannealed steel panel in FIG. 11 (a) was treated first with a 10%SafeGard™ CC-3400 permanganate solution applied in a bath at 140° F. forapproximately 4 seconds followed 24 hours later by the application of a10% SafeGard™ CC-4000 silicate solution at a bath temperature of 80° F.for approximately 4 seconds followed by a cold reduction in thicknessfrom 0.295″ to 0.244″, then subject to a 36 hour salt spray test inaccordance with ASTM B-117-07a and wherein FIG. 11 (b) was treated in amanner similar to FIG. 11( a) then subject to a 72 hour salt spray testin accordance with ASTM B-117-07a; and

FIG. 12 is a photographic depiction initially treated using a 0.8%permanganate solution at a bath temperature of 140° F. for about 4seconds followed by a 2.9% silicate solution at a bath temperature of80° F. for about 4 seconds followed by a cold reduction in thicknessfrom 0.030″ to 0.016″, a reduction of approximately 47% and illustratingless than 5% red rust after 140 hours of exposure in salt spray.

DETAILED DESCRIPTION OF THE DISCLOSURE

As used in this application, the term “zinc substrate” is intended tocover both zinc parts, and parts that are zinc-plated, particularlymetal products which have been galvanized, galvannealed, etc., asdiscussed previously. The terms “treating” or “coating” are intended tocover dipping, immersion, spraying alone or in combination with a zincsubstrate. The term “containing essentially no hexavalent or trivalentchromium cations or chromate anions” should be interpreted to mean thatthese chemical species are essentially not present in the coatingcompositions, although some minimal amounts may be present asimpurities. “Conversion coating” is a well-known term of the art andrefers to the replacement of native oxide on the surface of a metal bythe controlled chemical formation of a film or coating. The term Ultra®steel is a process of work hardening cold steel with work rolls to alterthe surface characteristics. Through this process, the effectivethickness of the material is increased to that of the original thicknessplus the depth of the ribbing. Patents pertinent to this process areU.S. Pat. Nos. 6,183,879 and 5,689,990 as well as Canadian Patent No.2,149,914.

The term “G-40” means a hot-dipped galvanized coating which complieswith ASTM C 645 Rev. A Standard Specification for non-structural steelframing members and C645, Specification for non-load (axial) bearingsteel studs, runners (track) and rigid furring channels for screwapplication of gypsum board. As known in the industry, the Ultra® steelprocess creates many radii and peaks and valleys in the steel. Anycoating must be strong and flexible so that it does not crack or peel orflake off. As known in the industry, the Ultra® steel process isactually done in a separate process that is located in front of the rollformer. Flat steel comes off an uncoiler and goes through the Ultra®process and then is roll formed in a regular roll former. In the seriesof Figures illustrated in FIG. 5, essentially every possible sample orposition in the Ultra® steel process was tested. The terms“approximately” and “about” mean within experimental error pertinent tothe steel industry.

Referring now to the drawings, a method described by making light gaugebuilding galvanized metal products, such as metal studs, which a thinnedcorrosion-resistant galvanized stud (preferably galvanized steel)including the steps of: (a) rolling a roll of galvanized steel by atleast 10% (e.g. 20%, or 25%); (b) forming said roll into at least onemetallic building component; (c) applying a permanganate composition(preferably an aqueous alkali metal) to at least one surface of thebuilding component (at a concentration ranging from 50% to fullstrength, 100%) containing essentially no hexavalent or trivalentchromium ions, wherein the preferred alkali metal permanganatecomposition has an alkali metal selected from the group consisting ofpotassium, sodium, lithium, rubidium and cesium and is applied at a pHof about from 9.0 to 2.0 inclusive, such that the building componentmeets the ASTM B 117-73 test and provides a corrosion resistance similarto a like building component made of the initial thickness without therolling step, (more preferably within 5%) of said building componentwhich had not been reduced in thickness. The method also includes thestep of (d) applying an silicate coating (preferably an inorganic alkalimetal silicate) to seal said permanganate composition on said at leastone side of said building component and wherein said alkali metal isselected from the same group previously identified. The silicate coatingmay be applied while the permanganate coating is drying.

Manganese Source:

Manganese is one non-toxic, non-regulated metal which ahs beenconsidered as a chromium or lead replacement. Manganese (like chromiumor lead) exhibits more than one oxidation state (Mn⁺², Mn⁺³, and Me⁺⁴).In addition, the oxidation-reduction potential is comparable to that ofCr(VI) or Pb(IV) in acidic solutions. For example, in acid solution:

Mn⁺³+e⁻→Mn⁺²+1.49 V

Mn⁺⁴+e⁻→Mn⁺³+1.65 V

Cr⁺⁶+3e⁻→Cr⁺³+1.36 V

Pb⁺⁴+2e⁻→Pb⁺²+1.70 V

The Mn(IV) and Mn(III) ions are very good oxidizing species withoxidation-reduction potentials of +1.65 V and +1.49 V (at pH=0),respectively. The hydroxyl and oxygen liberated from water when Mn(IV)or Mn(III) is reduced will oxidize nearby bare metal. This results in apassivated metal surface if sufficient oxygen is released. The potentialrequired to reduce tetravalent or trivalent manganese to divalentmanganese is only 0.29 v or 0.13 volts greater than that needed to addthree electrons to reduce Cr(VI) to trivalent chromium, Cr(III).Although neither Mn(IV) or Mn(III) match Pb(IV) in terms of redoxpotential, neither is significantly lower and so comparable passivationof metal is achieved. Mn(II) is formed during corrosion inhibition bythe oxidation of base metal in the presence of Mn(IV) or Mn(III) andwater. Mn(II) is similar to Cr(III) in that neither is particularlyeffective as redox-based corrosion inhibitors.

Manganese sources can be nearly any water, alcohol, or hydrocarbonsoluble manganese compound in which the manganese is in the divalent,trivalent, tetravalent, or heptavalent oxidation state. Water-solubleprecursors are typically used. Inorganic divalent manganese precursorcompounds include, but are not limited to, manganese nitrate, manganesesulfate, manganese perchlorate, manganese chloride, manganese fluoride,manganese bromide, manganese iodide, manganese bromate, manganesechlorate, and complex fluorides such as manganese fluosilicate,manganese fluotitanate, manganese fluozirconate, manganese fluoborate,and manganese fluoaluminate. Organometallic divalent manganese precursorcompounds include, but are not limited to, manganese formate, manganeseacetate, manganese propionate, manganese butyrate, manganese valerate,manganese benzoate, manganese glycolate, manganese lactate, manganesetartronate, manganese malate, manganese tartrate, manganese citrate,manganese benzenesulfonate, manganese thiocyanate, and manganeseacetylacetonate.

The manganese source may be a compound with the manganese in theheptavalent oxidation state (permanganates). Heptavalent manganeseprecursors include, but are not limited to: potassium permanganate,sodium permanganate, lithium permanganate, ammonium permanganate,magnesium permanganate, calcium permanganate, strontium permanganate,barium permanganate, zinc permanganate, ferric permanganate, nickelpermanganate, copper permanganate, cobalt permanganate, ceriumpermanganate, lanthanum permanganate, yttrium permanganate, and aluminumpermanganate.

Oxidation Source:

If Mn(III) and/or Mn(IV) compounds are produced via precipitation, anoxidizing species will typically be included in the synthesis solutionif divalent manganese compounds are used as precursors for Mn(III) andMn(IV). Additional amounts of oxidizer may be added to help control andmaintain a desired amount of Mn(III)/Mn(IV) in the solution byreoxidizing Mn(III)/Mn(IV) that has become reduced. The trivalentmanganese ion is an exceptionally good oxidizing species with anoxidation-reduction potential of +1.49 V at a pH of 0 for theMn(III)-Mn(II) couple in water, and the tetravalent manganese ion is aneven stronger oxidizing species, with a redox potential of +1.65 V undersimilar conditions. Strong oxidizers are required because of the highpotential of their redox reaction. The oxidizers may be gases, liquids,or solids. Solid oxidizers are typically used for this application dueto ease of handling and reagent measurement. Other starting materials(manganese source and stabilizer source) will also frequently be solids.Liquid oxidizers may be used, but handling and accurate process meteringhave proven difficult. Gaseous oxidizers may be the most cost effectiveand chemically efficient on a large scale, but are also the mostproblematic due to handling and venting concerns.

Oxidizers suited for the purpose of producing and maintaining themanganese ion in the trivalent or tetravalent charge state include butare not restricted to peroxides and peroxo compounds (includingsuperoxides, persulfates, perborates, permitrates, perphosphates,percarbonates, persilicates, peraluminates, pertitanates, perzirconates,permolybdates, pertungstates, pervanadates, and organic peroxyacidderivatives), ozone, hypochlorites, chlorates, perchlorates, nitrates,nitrites, vanadates, iodates, hypobromites, chlorites, bromates,permanganates, periodates, and dissolved gases such as oxygen, fluorine,or chlorine. Inorganic and organic derivatives of these compounds may beused. Typical oxidizers for this use are peroxides, persulfates,perbenzoates, periodates, bromates, hypochlorites, gaseous dissolvedoxygen, and even the oxygen content of air. In general, any inorganic,organic, or combination species with an oxidation potential of +1.0 V orgreater (at a pH of 1) will be capable of oxidizing divalent manganeseto the trivalent or tetravalent oxidation state.

Valence Stabilizers:

In some embodiments (although optional), a valence stabilizer isoptionally added to establish an electrostatic barrier layer around thecation-stabilizer compound in aqueous solution. The valence stabilizeralso provides a timed release of the inhibitor ion, as well as ensuringthat the oxidative strength will not be reduced too rapidly. Thus, avalence stabilizer is preferred for the trivalent or tetravalentmanganese ion because of its reactivity and to produce controlledtrivalent or tetravalent manganese solubilities. Stabilization helpsavoid reduction and premature conversion of the ion to the divalentcharge-state during compound formation, carrier incorporation,application, and exposure to a corrosive environment. Stabilizerscontrol solubility, mobility, ion exchange, binder compatibility, andthe degree of surface wetting. The exact solubility of this compound maybe modified by species released into solution by the dissolving metalsurface or by the subsequent addition of solubility control agents. Avariety of inorganic and organic stabilizers are available that canserve to control solubility. The stabilizer may also act as anion-exchange host and/or trap for alkali or halide ions in solution.

Any material in the synthesis bath which complexes with trivalent ortetravalent manganese (whether inorganic or organic) and which resultsin the formation of a Mn(III) or Mn(IV) containing compound that exhibitsuitable solubility can serve as a valence stabilizer for trivalent ortetravalent manganese. The assembly of a protective shell around thehighly charged Mn(III) or Mn(IV) and its associated oxygen and hydroxylspecies can help control the rate at which the manganese is reduced andits oxygen is released. Proper selection of materials for forming theprotective shell will allow solubility tailoring of the entire assemblyto its intended application environment. Valence stabilizers describedabove may need some type of additional solubility control to increasethe performance of the trivalent or tetravalent manganese-valencestabilizer compound. Additional solubility control agents may be in theform of inorganic or organic compounds. Their use is optional ratherthan a requirement for effective valence stabilization and solubilitycontrol.

Inorganic valence stabilizers are formed around the Mn(III) or Mn(IV)ion by “polymerizing” in synthesis solution. Inorganic stabilizersinclude molybdates (Mo⁺⁶, Mo⁺⁵, or Mo⁺⁴, for example [Mn⁺⁴Mo₉O₃₂]⁶⁻ and[Mn⁺⁴Mo₁₂O₄₀]⁴⁻), tungstates (W⁺⁶, W⁺⁵, or W⁺⁴, for example[Mn⁺⁴W₁₂O₄₀]⁴⁻ and [Mn⁺³ ₂W₂₂O₇₄]¹⁰⁻), vanadates (V⁺⁵ and V⁺⁴, forexample [Mn⁺⁴V₁₃O₃₈]⁷⁻ and [Mn⁺⁴V₁₁O₃₂]⁵⁻), niobates (Nb⁺⁵ and Nb⁺⁴, forexample [Mn⁺⁴Nb₁₂O₃₈]¹²⁻), tantalates (Ta⁺⁵ and Ta⁺⁴, for example[Mn⁺⁴Ta₁₂O₃₈]¹²⁻), tellurates (Te⁺⁶ and Te⁺⁴, for example[Mn⁺⁴Te₃O₁₈]¹⁴⁻), periodates (I⁺⁷, for example [Mn⁺⁴I₃O₁₈]¹¹⁻), iodates(I⁺⁵, for example [Mn⁺⁴I₆O₁₈]²⁻), antimonates (Sb⁺⁵ and Sb⁺³), stannates(Sn⁺⁴), sulfates (S⁺⁶, such as manganese spinels [Mn⁺³(SO₄)₂]¹⁻), andpolyphosphates (P⁺⁵, for example [Mn⁺³P₃O₁₀]²⁻ and [Mn⁺³P₂O₇]¹⁻). Manyof these inorganics form octahedral and square pyramidalheteropolymetallate structures on precipitation from solution. Forexample, tellurate ions begin to polymerize near pH 5 in water and willcomplex with Mn(III) or Mn(IV) ions in basic solution pH's. Therefore,as the pH is raised in the pigment synthesis bath, the tellurate ionpolymerizes to polymorphs, which then complex the Mn(II) or Mn(IV) ion.

The most notable valence stabilizer for low and insoluble Mn(III) andMn(IV) is oxygen (O), as evidenced by the natural stability of suchcompounds as MnO₂, Mn₃O₄, Mn₂O₃ and MnOOH, all of which contain Mn(III)and/or Mn(IV) ions. In instances where oxygen is used as a valencestabilizer for Mn(III) or Mn(IV), differences in addendum cations (i.e.,Ca⁺² in CaMn₂O₄ or Zn⁺² in ZnMn₂O₄) are observed to alter the solubilityof the formed compound, and its performance as a corrosion inhibitor ina given binder system.

Additional valence stabilizers silicates (Si⁺⁴, for example[Mn⁺³Si₂O₆]¹⁻), borates (B⁺³, for example Mn⁺³ ₂B₄O₉), phosphates (P⁺⁵,for example Mn⁺³PO₄), titanates (Ti⁺⁴), zirconates (Zr⁺⁴), andaluminates (Al⁺³). These compounds can also form octahedral or squarepyramids, but have a higher tendency to form chain-like structuresduring calcining or firing. Combinations of these materials, such asphosphosilicates, aluminosilicates, or borosilicates may also functionas valence stabilizers for Mn(III) and Mn(IV) compounds.

Surface Activators:

Insome embodiments, (although optional), a surface activator is added tothe first coating composition in order to assist the formation ofcoatings at a commercially useful rate. This typically is achieved inthe presence of an ion which performs an oxidizing function and enhancesthe rate of reaction. Compounds providing such ions are often referredto as activators, which typically supply anions such as sulfate,nitrate, sulfamate, fluoride, acetate and formate, usually as salts ofsodium or other alkali metals. Such traditional activators can beincluded in the bath at concentrations for each between about 0.1 gm/land 5 gm/1.

Suitable for use in combination with or in place of these traditionalactivators are the class of organic activating agents according to thisinvention, which can be considered to be accelerating activators thatare capable of further enhancing the quality and the rate of coatingformation beyond that provided by the traditional activators. Theseorganic activating agents, in addition, operate in the nature of acomplexing agent in order to assist in keeping the coating-formingagents in solution. Such organic compounds typically take the form ofcarboxylic acids or their bath-soluble derivatives, usually salts, whichgenerally have functional groups in addition to those provided bymonocarboxylic acids or derivatives such as acetates or formates.Included are compounds having between about 2 and 12 carbon atoms thatare polyhydroxy carboxylic acid compounds, for example heptagluconate,or polycarboxylic acid compounds such as oxalic acid, its derivatives,analogues or homologues including the oxalate, malonate, and succinategroups. The compounds may be of the structure: XOOC(CH₂)_(n)COOX,wherein n is 0 or 1, and X is hydrogen, alkali metal, ammonium, or analkali metal-transition element complex. Organic activating agents aremost conveniently provided as potassium-titanium complex salts or alkalimetal carboxylic acid salts. Bath concentrations range as high as 7.5gm/l, especially for compounds having polycarboxylic acid groups such asheptagluconate, and may be between about 0.25 and about 4.5 gm/l of thetotal bath volume for the polycarboxylic or oxalic acid type ofcompounds.

Buffers:

While optional, certain of the activators, especially those that havemultiple carboxylic acid groups, can be present in the bath as a bufferto maintain a desired bath pH range while passivating large surfaceareas, it is often desirable to include a separate buffering agent assuch within the composition. To facilitate handling of the total bathingredient composition before incorporation into the bath, the bufferingagent should be powdered, granulated, or the like and readily dissolvedin an aqueous acidic bath. Boric acid is an exemplary buffering agent.Bath concentrations generally do not have to exceed about 5 gm/l, andmay be within the range of about 0.25 to about 2.0 gm/l of bath.

As shown in the drawings is a series of rolled panels which have beenexposed to various numbers of hours of salt spray exposure. The testpanels have been reduced in thickness from a base thickness of about 28mils to about 24 mils, to about 22 mils, or to about 21 mils, and coatedwith the alkali metal permanganate composition at a concentration of 0%(no coating); about 20% concentration; about 50% concentration; andabout 80% concentration of undiluted composition.

In some embodiments, the process includes a method for the coating ofzinc or zinc coated (e.g., galvanized or aluminized or subjected to aGalvalume® process or galvannealed processing) articles with acomposition containing an alkali metal permanganate composition at a pHof about 9.0 to 2.0. The passified zinc or zinc coated article has achromium-free permanganate protective conversion coating. As used inthis disclosure, a conversion coating is one that reacts quickly withzinc and is more than a barrier coating, but performs as a conductiveconversion coating. Without being held to one theory of operation, it isbelieved that at the molecular level, the conversion coating reactsquickly with zinc forming either a chemical bond, or an associativebond, thereby rendering it more in the nature of a conversion coating,rather than a simply barrier coating.

The alkali metal in the alkali metal permanganate composition isselected from the group consisting of lithium (Li), sodium (Na),potassium (K), cesium (Cs) and rubidium (Rb). The preferred alkali metalis potassium. The concentration of permanganate necessary to produce anacceptable coating is a minimum of 0.001 moles per liter. With potassiumpermanganate, this is essentially about 0.16 grams per liter. Themaximum concentration of the permanganate composition is the saturationpoint of the salt being used. The solution may have a temperatureranging from about the freezing point of the solution to its boilingpoint. The preferred temperature range is 60° F. to 180° F. As thetemperature of the solution rises, less immersion time is required toform a corrosion resistant coating on the surface of the zinc. Theimmersion time for preparing a corrosion-resistant coating on a zincsurface is about 2 seconds to 3 minutes at 80° F.-160° F. Preferredimmersion times are approximately 4-5 seconds at 140° F.

An alternative to immersion coating is spraying of the permanganatecomposition. The applicable parameters will have to be adjusted as isknown within the skill in the art to make these adjustments to theprocess parameters.

Once again, without being held to one theory of operation, it isbelieved that at the molecular level, the conversion coating reactsquickly with zinc substrate forming either a chemical bond, or anassociative bond, thereby rendering it more in the nature of aconversion coating, rather than a simply barrier coating, and therebymodifies the surface energy of the zinc substrate. The inclusion of asurfactant impacts the ability to further wet the surface of the zincsubstrate. It is believed that the manganese, which is similar in sizeto chromium, forms various molecular complexes at the surface of thezinc substrate, which upon the sequential application of a silicatecoating (preferably without drying interposed therebetween) will furtherresult in a concentration gradient coating in which the permanganatecoating and silicate coating form an interfacial bond.

The invention of the application will be better understood by referenceto the following examples which serve to illustrate but not to limit thepresent invention.

Example #1

A series of galvannealed panels are conversion coated prepared in accordwith the following steps. An alkaline phosphate cleaner (e.g., Sanchem™500) is used to clean any residual oils, dirt, or foreign matter fromthe coating surface, leaving a fresh surface to conversion coat. An acidrise is applied to give the surface a mild acidic character so that itis receptive to the reaction between the zinc and the potassiumpermanganate moiety (e.g., Safegard™ CC-3400). In a further embodiment,the pH of the acid solution will range from 2 to 9, preferably 3 to 8.The permanganate moiety composition (e.g., Safegard™ CC-3400) is appliedto the surface of a series of thinned panels ranging in thickness from0.028″ (28 mils) to 0.021″ (21 mils) using permanganate concentrationsranging from 0% (no conversion coating) to 80% (20% diluted) conversioncoating as compared to an undiluted concentration. The panels werethinned using well-known thinning methodology, e.g., counter-rotatingdrums. The panels were lastly coated with an inorganic water glasssealant coating (Safegard™ CC-4000) by immersion in a potassium silicatesolution (8.3% K₂O and 20.8% SiO₂ with a SiO₂/K₂O ratio of about 2.5,29.1% solids with viscosity of 40 centipoises) at room temperature, toas high as 195-212° F. for up to one minute. The panel was removed fromthe silicate solution and rinsed with deionized water. The panel wasthen placed in a salt-fog at 95° F., according to ASTM Standard B-117.After 75 hours of exposure, the panel showed only minor pitting. Thepanels (about 6″×12″) were subjected to continuous salt spray for 24 to75 hours in accordance with ASTM B 117-73, photographic evidence of theresults being illustrated in FIGS. 1-4 (a) through (c).

FIGS. 1( a) through 1(c) illustrate the control experiment in which thegalvanized panel was not thinned prior to the application of thepermanganate moiety which was added at a concentration ranging from 0%(no permanganate application) to 20% (80% diluted) permanganateapplication to 50% (50% diluted) permanganate application to 80% (20%diluted) permanganate application.

FIGS. 2( a) through 2(c) illustrate the impact of an approximate 15%reduction in thickness of the panel from its initial 28 mil thicknessand associated impact on corrosion resistance. Only the panels to whichthe application of at least 50% permanganate moiety has been added meetthe ASTM specification.

FIGS. 3( a) through 3(c) illustrate the further impact of an approximate20% reduction in thickness of the panel from its initial 28 milthickness and associated impact on corrosion resistance. In a mannersimilar to that described for FIG. 2, only the panels to which theapplication of at least 50% permanganate moiety has been applied meetthe ASTM specification.

FIGS. 4( a) through 4(c) illustrate the further impact of an approximate25% reduction in thickness of the panel from its initial 28 milthickness and associated impact on corrosion resistance. In a mannersimilar to that described for FIGS. 2 and 3, only the panels to whichthe application of at least 50% permanganate moiety has been appliedmeet the ASTM specification.

Example #2

As illustrated in FIGS. 5 (a) through FIGS. 8 (n), a series ofphotographic depictions of steel panels are provided, ranging in timeexposed to a salt spray exposure from 24 hours to 96 hours. The firstpanel illustrated in (a) is a certified G-40 sample derived from flatsteel used as a test comparative known to meet ASTM specification ofG-40 for non-structural framing. The second panel illustrated in (b) isa head end of slit coil used for formed Ultra® steel sample which hadbeen galvannealed with A45 coating and reduced in thickness from 0.029″to 0.0245″. The third panel illustrated in (c) is a second sample of atail end of slit coil used for formed Ultra® steel sample. The fourthpanel illustrated in (d) is a head end of slit coil used for formed flatsteel sample which had been galvannealed with A45 coating and reduced inthickness from 0.029″ to 0.0245″. The fifth panel illustrated in (e) isa second sample of a tail end of slit coil used for formed flat steelsample. The sixth panel illustrated in (f) is an additional tail end ofslit coil sample used for formed flat steel sample. The seventh panelillustrated in (g) is a flat steel sample of cold worked with Ultra®steel process before forming into a stud (head of coil). The eighthpanel illustrated in (h) is a second sample of flat cold worked withUltra® steel process before forming into a stud (head of coil). Theninth panel illustrated in (i) is a flat steel sample of cold workedwith Ultra® steel process before forming into a stud (tail of coil). Thetenth panel illustrated in (j) is a second sample of flat cold workedwith Ultra® steel process before forming into stud (tail of coil). Theeleventh panel illustrated in (k) is a sample of formed Ultra® steelstud (head of coil). The twelfth panel illustrated in (l) is a sample offormed Ultra® steel stud (tail of coil). The thirteenth panelillustrated in (m) is a sample of formed flat steel stud (head of coil)and the fourteenth panel illustrated in (n) is a sample of formed flatsteel stud (tail of coil).

The panels shown in FIGS. 7 (g) through 7 (l) had about 5% red rust at75 hours of salt spray exposure. These panels continued to corrode asillustrated in FIGS. 8 (g) through 8 (l) with approximately 25% red rustat 96 hours of salt spray exposure.

The G-40 certified sample is G-40 from a piece of flat steel used togauge the performance of a test sample to a know sample and a samplethat meets the ASTM specification of G-40 or equivalent fornon-structural framing. For the panels designated as the second panelthrough the fourteenth panel above, the panels were cold reduced to a45A coated galvannealed coil from 0.0296″ to 0.0245″ (Ultra® steeltypically least thickness). Cold working stresses and bends and embossesthe steel to a large degree. By subjecting the coating to the “Ultra®steel process”, processing which is more rigorous than typicalprocessing such as would occur in regular roll forming, the beneficialresults of this invention are achievable in a less rigorous environment.As the above testing indicates, the process will stand up to the coldreduction and will stand up to the Ultra® steel process and then can beroll-formed into a C-stud.

As mentioned previously, and as used in this application, the term“Ultra® steel process” is that which is discussed and described in U.S.Pat. Nos. 6,183,879 and 5,689,990. This process provides a method ofproducing lightweight thin metal sheet that is flexure resistant, inwhich the method includes passing flexible sheet material of relativelythin gauge between two rolls each having teeth, each tooth having fourflanks, each flank facing in a direction between an axial direction anda circumferential direction, the teeth having rounded corners, the rollsbeing arranged so that the teeth of one roll extend into gaps betweenteeth on the other, the rolls being rotated at substantially the samespeed about generally parallel axes to form rows of projections on bothfaces of the sheet passed therethrough without damage to the surfacematerial of the sheet.

When flexible sheet material of relatively thin gauge is passed in thenip between rollers having teeth, the sheet surface can be damaged sothat fragments of the sheet come away and accumulate in the spacesbetween teeth. The fragments then cause further damage to the sheetmaterial which is following behind. The teeth may be rounded in twoareas: at the corners of the peak and at the peak. By rounding thecorners of the teeth, typically both at the peak and the root thereof,it is possible to cause the sheet material to flow in the clearancebetween opposed teeth to become more rigid with little or no thinningand without spalling of the sheet material or of the teeth. As a resultthe rolls suffer less wear and need less cleaning and last longer; thesheet material is rigid and yet lightweight.

The corners of the teeth may be rounded in the range from about 0.05 to15 mm, and may be in the range of 0.15 to about 4 mm. The extent ofradius is related to the size of the tooth which in turn relates to thegauge of the sheet being processed. Where the tooth is relatively smallfor use with thin gauge sheet, the corner radius is about 0.2 and thepeak may be about 1 mil; where the tooth is relatively large for thickergauge sheet the corner radius is about 1 mil and the peak about 2.5. Theratio of the corner radius to the peak radius thus decreases withincreasing size of the tooth. It has been observed that outside theseparameters the tooth tends to have corners which can cut into thesurface of the sheet material being treated. By virtue of the roundingof the corners and the peaks of the teeth there is no risk that a sheetwill occur. Such cracking releases fragments of the sheet material whichtend to foul the space between the teeth of the roll which risk breakingthe integrity of the surface of the sheet following on behind. Inpracticing the method of the invention, not only does the sheet surfacemaintain its integrity but the formed sheet undergoes an enhancedstiffening effect as a result of which the mechanical strength, e.g.rigidity of the sheet is enhanced. The method may even be applied to athin flexible sheet carrying a coating, e.g. a paint or like filmwithout risk that it will be harmed.

The Ultra® process also provides a set of rolls, rows of teeth beingpresent on the outer surface of the rolls, each tooth having four flanksof involute form, and each flank facing in a direction between an axialdirection and a circumferential direction, the corners of the teethbeing radiused as defined.

The Ultra® process also provides sheet material having projections onboth of its surfaces, a corresponding depression being on the surfaceopposite each projection, the relative positions of the projections anddepressions being such that lines drawn on the surface are non-linear,the sides of the projections lying a line extending between alongitudinal direction and a lateral direction, the overall distancebetween adjacent projections and depressions being within the range of 2μm to 5 mm and in the range of four to ten times the gauge, wherein thecorners of the projections and depressions are radiused.

The embossing which is described in U.S. Pat. No. 5,689,990 is alsoapplicable to the coatings of this method. As discussed in the '990patent, sheet material is used having on both of its faces a pluralityof rows of projections, each projection having been formed by deformingthe sheet material locally to leave a corresponding depression at theopposite face of the material. For example there extends in a firstdirection, rows of alternating projections and depressions and straightlines which can be drawn on a surface of the material between adjacentones of these rows. The projections and depressions also form rows whichextend in a second direction substantially perpendicular to the firstdirection and between which further straight lines can be drawn on thesurface of the material. Along these straight lines, the overallthickness of the material is substantially equal to the thickness of theplain sheet material from which the material is formed and the materialcan bend along these lines considerably more easily than it can bendalong a centerline of one of the rows. The overall thickness of thesheet material is approximately twelve times the thickness at a pointwhere the thickness has a maximum value, and which thickness is thegauge of the material.

According to one aspect of the '990 disclosure, sheet material isprovided wherein the relative positions of the projections anddepressions are such that lines drawn on a surface of the materialbetween adjacent rows of projections and depressions are notrectilinear. The overall thickness of the sheet material as viewed inany cross-section in a plane which is generally perpendicular to thesheet material is substantially greater than the gauge of the material.In cross section, sheet material is undulatory and there is no placewhere the material can be cut along a straight line and the resultingcross section of the material will be rectilinear.

The overall thickness of the sheet material is determined by the heightsof the projections at both faces of the material. The height ofprojections which is sufficient to ensure that lines drawn on a surfaceof the material between adjacent rows of projections and depressions arenot rectilinear depends upon the pitch of the projections anddepressions in the rows. It was found that an overall thickness of twicethe gauge of the sheet material is generally a suitable thickness andsufficient to avoid rectilinear lines on the surface of the material.The overall thickness may not be more than four times the gauge of thematerial, or may not exceed more than three times the gauge of thematerial.

By limiting the overall thickness of the material to a value which isjust sufficiently great to avoid the presence of rectilinear lines oneither surface of the material, it was found that it was possible toavoid reducing the overall length of the sheet material significantlyduring formation of the projections. The spacing between the crests ofadjacent projections at each face of the material may exceed three timesthe dimension of each of those crests measured in the same direction assaid spacing.

The projections at each face can be assigned to a variety of rows, forexample rows extending along the material, rows extending across thematerial at right angles and rows extending across the materialobliquely to the length of the material. In the row with the smallestpitch, the pitch (called herein the minimum pitch) may be within therange 2 mm to 5 mm. The pitch may be within the range four to ten timesthe gauge of the material. It was found that a pitch may beapproximately six times the gauge of the material, in a case where theoverall thickness is approximately twice the gauge, avoids the presenceof rectilinear lines on either surface of the material and therebyachieves a substantial improvement in bending strength, as compared withthe plain sheet material from which the material embodying the inventionis formed, without any significant increase in the mass of material persuperficial unit of area. In the case where elongated sheet material isused, each projection may be a plurality of flanks facing in respectivedirections which are neither along the material nor perpendicular to thelength of the material.

Example #3

As illustrated in FIGS. 9 (a) and 9 (b), two galvanized test panels weresequentially treated with Safegard™ CC-3400 followed approximately 10minutes later by Safegard™ CC-4000 with one panel subsequently beingbent to 60-75° and then subjected to a 75 hour salt spray test inaccordance with ASTM B-117-07a. The experimental tests indicate that thecoatings maintained their integrity even after the application of asevere bending stress.

Example #4

As illustrated in FIGS. 10 (a) and 10 (b), two galvannealed steel panelswere subject to a 75 hour salt spray test in which the panel in FIG. 10(b) was treated by a sequential combination of a 0.8% permanganatesolution at a bath temperature of 140° F. for about 4 seconds followedby a 2.9% silicate solution at a bath temperature of 80° F. for about 4seconds followed by a cold reduction in thickness from 0.029″ to 0.021″,while FIG. 10 (a) illustrates a steel panel which was not subject to anypretreatment and subject to a 75 hour salt spray test in accordance withASTM B-117-07a. The value of the coating is evident from the largeformation of rust on the untreated panel illustrated in FIG. 10 a whichcorroded badly after just 24 hours.

Example #5

As illustrated in FIGS. 11 (a) and 11 (b), the impact of drying timebetween the sequential application of the coating with permanganatesolution and silicate solution is shown. By lowering the time betweencoats, a synergistic effect is clearly shown. Applying the two coatingswith a 24 hour separation between resulted in a panel which did not pass36 hours of salt spray testing. However, applying the same two coatingswith a 10 minute separation between, resulted in a panel which passed 72hours of salt spray testing. Without being held to any one theory ofoperation, it is believed that a chemical bond is formed between themetallic permanganate coating and the silicate coating.

Example #6 Comparative Example

A series of silicates were coated onto zinc plated steel for salt spraycorrosion resistance. In this experiment, a six inch by six inch steelpanel with a 0.001 inch thick film of electrodeposited zinc was cleanedin a strong alkaline cleaner at 150° F., rinsed in deionized water,placed in a 1% nitric acid solution for 30 seconds (to remove unwantedmetal oxides), rinsed in deionized water for a second time, and thenplaced in a 1% potassium silicate solution for 60 seconds at 140° F.,removed, rinsed and then allowed to dry. The panel was allowed to sitfor one day, then placed in a neutral salt spray cabinet operated inaccordance with ASTM specification B 117. Red rust formed within eighthours.

Example #7 Comparative Example

The experimental procedure outlined in Example #6 was repeated with a 5%potassium silicate solution. Red rust formed within 12 hours.

Example #8 Comparative Example

The experimental procedure outlined in Example #6 was repeated with a10% potassium silicate solution. Red rust formed within 12 hours.

Examples #6 through #8 illustrate the point that the invention requiresat least a first coating of permanganate or molybdate, followed by asecond coating of silicate. The application of a silicate coating byitself was insufficient to achieve the desirable characteristics of theinvention.

Example #9

Two galvanized panels that were initially treated using a 0.8%permanganate solution at a bath temperature of 140° F. for about 4seconds followed by a 2.9% silicate solution at a bath temperature of80° F. for about 4 seconds followed by a cold reduction in thicknessfrom 0.030″ to 0.016″, a reduction of approximately 47% and illustratingless than 5% red rust after 140 hours of exposure in salt spray.

Therefore what has been shown is that using the technique of thinningsaid panels by at least 10%, e.g. 20%, or 25%, or ˜50% and coating saidthinned panels with a molybdate moiety ranging in concentration of from50%-100%, a performance similar to an panel which has not been reducedin original thickness is achieved according to ASTM B 117-73. By similarperformance, it is understood for purposes of this application, thetesting protocol will result in a test result which is about the same,and within 25% performance with a similarly coated panel which had notbeen thinned. The performance may be within 15%, or within 5%.

Therefore, what has been described in general is a methodology by whicha thinned corrosion-resistant stud (preferably comprising a zinccoating, more preferably galvanized steel) is capable of achievingcorrosion-resistance similar to a metal stud which has not been thinned,the method including the steps of: (a) thinning a roll of galvanizedsteel by at least 10% (more preferably 20%, most preferably 25%, andoptionally up to ˜50%); (b) forming said roll into at least one metallicstud; (c) applying a permanganate conversion coating composition (at aconcentration ranging from 50% to full strength, 100%) containingessentially no trivalent or hexavalent chromium, said permanganatecomposition may comprise an alkali metal permanganate compositionwherein said alkali metal is selected from the group consisting of Li,Na, K, Cs and Rb or a mixture thereof to said stud at a pH of about 9.0to about 2.0 inclusive; (d) applying an inorganic silicate coating toseal said permanganate composition on said stud; and (e) testing saidpanel in accordance with ASTM B 117-73 and achieving a performance withsaid thinned stud within no worse than 25% (e.g. within 15%, or within5%) of a stud which had not been reduced in thickness. It is recognizedthat the step of thinning above may be performed either before thesequential application of coatings as illustrated above, or may beperformed after the sequential application of coatings.

Also described is a process for making a corrosion-resistant buildingcomponent comprising the steps of providing a steel sheet suitable foruse in making metal building components, said sheet having a surfacecomprising zinc or a zinc alloy, suitable for use in making metalbuilding components having an initial thickness, forming said rolledsteel sheet into at least one metal building component, applying a firstcoating composition comprising an alkali metal permanganate compositioncontaining essentially no chromium to said building component, andwherein said alkali metal of said alkali metal permanganate compositionis selected from the group consisting of potassium, sodium, lithium,rubidium and cesium and applied at a pH of about 9.0 to 2.0 inclusive,and applying a second coating composition comprising an alkali metalsilicate sealant composition wherein the alkali metal is selected fromthe group consisting of potassium, sodium, lithium, rubidium and cesiumsuch that the building component meets the ASTM C 645-08a at a coatingweight which is equal to or less than that specified by ASTM A 1003-G40.

A process is also described by which building components which do notmeet ASTM coating weight requirements, (e.g., G-40 or equivalent fornon-structural) are coated so that the applicable standards are met.

In the foregoing description, certain terms have been used for brevity,clearness and an aid to understanding the technology; but no unnecessarylimitations are to be implied there from beyond the requirements of theprior art, because such terms are used for descriptive purposes and areintended to be broadly construed. Moreover, the description andillustration of the invention is by way of example, and the scope of theinvention is not limited to the exact details shown or described. Thisinvention has been described in detail with reference to specificembodiments thereof, including the respective best modes for carryingout each embodiment. It shall be understood that these illustrations areby way of example and not by way of limitation.

1. A process for making a corrosion-resistant metal building componentcomprising the following steps, regardless of order, of: providing asteel sheet, said sheet having a surface comprising zinc or a zincalloy, suitable for use in making metal building components having aninitial thickness, rolling the steel sheet by at least 10% to form athinner steel sheet, forming said rolled steel sheet into at least onemetal building component, applying a permanganate coating compositioncontaining essentially no trivalent or hexavalent chromium to saidbuilding component, at a pH of about 9.0 to 2.0 inclusive; and applyingan inorganic silicate coating to seal said permanganate composition onsaid building component, such that the building component meets the ASTMB 117-07a test and provides a corrosion resistance similar to a likebuilding component made of the initial thickness without the rollingstep.
 2. The process of claim 1 wherein said building component isselected from the group consisting of galvanized, galvalumed orgalvannealed.
 3. The process of claim 2 where further comprises a stepof adding a valence stabilizer to said permanganate composition.
 4. Theprocess of claim 1 where the percent rolling is at least 20%.
 5. Theprocess of claim 4 where the percent rolling is at least 25%.
 6. Theprocess of claim 1 which further comprises the step of adding a surfaceactivator prior to said step of adding a permanganate composition. 7.The process of claim 1 wherein said inorganic silicate coating is apotassium silicate.
 8. A process for making a corrosion-resistantgalvanized light gauge metal building stud comprising the followingsteps, regardless of order, of: providing a galvanized steel sheethaving an initial thickness of approximately 0.0295 inches or less;rolling the steel sheet by at least 10% to form a thinner galvanizedsteel sheet; forming said rolled steel sheet into at least one lightgauge metal stud; applying a permanganate conversion coating compositioncontaining essentially no trivalent or hexavalent chromium to saidbuilding component, said permanganate composition applied at a pH ofabout 9.0 to 2.0 inclusive; and applying an inorganic silicate coatingto seal said permanganate composition on said building component, suchthat the metal stud meets the ASTM B 117-07a test and provides acorrosion resistance similar to a metal stud made of the initialthickness without the rolling step.
 9. The process of claim 8 where thepercent rolling is at least 20%.
 10. The process of claim 9 where thepercent rolling is at least 25%.
 11. The process of claim 8 where saidpermanganate composition is applied at a concentration diluted to up toabout 50% of an undiluted composition.
 12. The process of claim 8wherein said coating is a potassium silicate.
 13. A process for making acorrosion-resistant building component comprising the following steps,regardless of order, of: providing a steel sheet suitable for use inmaking metal building components, said sheet having a surface comprisingzinc or a zinc alloy, suitable for use in making metal buildingcomponents having an initial thickness, applying a first coatingcomposition comprising an alkali metal permanganate compositioncontaining essentially no chromium to said building component, andwherein said alkali metal of said alkali metal permanganate compositionis selected from the group consisting of potassium, sodium, lithium,rubidium and cesium and applied at a pH of about 9.0 to 2.0 inclusive;applying a second coating composition comprising a silicate sealantcomposition to the building component; reducing a thickness of saidsteel sheet by at least 10%; forming said reduced thickness steel sheetinto at least one metal building component and wherein said buildingmaterial meets the ASTM B 117-07a corrosion-resistance standard at acoating weight which is equal to or less than that specified by ASTM A1003-G40.
 14. The process of claim 13 where building component is anon-structural light gauge galvanized metal building stud.
 15. Theprocess of claim 13 where said permanganate composition is applied at aconcentration diluted to up to about 50% of an undiluted composition.16. The process of claim 13 wherein said alkali metal is K in both saidalkali metal permanganate and said alkali metal silicate.